Flexible-to-rigid tubing

ABSTRACT

A flexible-to-rigid tube is flexible when routed and is then rigidized to increase burst strength. According to the preferred embodiments of the present invention, the flexible-to-rigid tube is included in a cooling plate assembly for transferring heat from electronic components mounted on a circuit board. In one embodiment, the flexible-to-rigid tube (while in a flexible state) includes a polydimethylsiloxane (PDMS) or other silicone containing pendant or terminal epoxy, vinyl and/or acrylate functional groups and an initiator (e.g., a sulfonium salt photoinitiator, a free radical photoinitiator, or a thermal initiator). In another embodiment, triallyl isocyanurate (TAIC) and an initiator are incorporated into a conventional PVC-based tubing material. The flexible-to-rigid tube changes from the flexible state to a rigid state via formation of a cross-linked network upon exposure to actinic radiation or heat.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates in general to the field of electronicpackaging. More particularly, the present invention relates toelectronic packaging that removes heat from one or more electroniccomponents using a cooling plate assembly having tubing through which acoolant flows and which is flexible when placed and is then “rigidized”to increase burst strength. The present invention also relates toflexible-to-rigid tubing for use in cooling plate assemblies and otherapplications.

2. Background Art

Electronic components, such a microprocessors and integrated circuits,must operate within certain specified temperature ranges to performefficiently. Excessive temperature degrades electronic componentfunctional performance, reliability, and life expectancy. Heat sinks arewidely used for controlling excessive temperature. Typically, heat sinksare formed with fins, pins or other similar structures to increase thesurface area of the heat sink and thereby enhance heat dissipation asair passes over the heat sink. In addition, it is not uncommon for heatsinks to contain high performance structures, such as vapor chambersand/or heat pipes, to enhance heat spreading into the extended areastructure. Heat sinks are typically formed of highly conductive metals,such as copper or aluminum. More recently, graphite-based materials havebeen used for heat sinks because such materials offer severaladvantages, such as improved thermal conductivity and reduced weight.

High performance computer systems have rapidly migrated toward liquidcooling solutions to effectively remove the massive heat load from theCEC, or central electronics complex. Typically, the CEC of a highperformance computer system includes CPUs, RAM and other electroniccomponents that generate copious amounts of heat. Heat is removed fromone or more electronic components in the CEC of high performancecomputer systems using a cooling plate assembly through which a coolantflows. The design of such systems typically calls for flexible tubingincorporating a large number of connections to one or morecoldplates/heat sinks.

For example, a plurality of articulated-gap coldplates may be employedin high performance computer systems. Individual articulated-gapcoldplates are separately spring-loaded against the top side of eachcomponent (or module) to be cooled. These individual articulated-gapcoldplates are interconnected with flexible tubing between eachcoldplate. Such a scheme is disclosed in U.S. Patent ApplicationPublication 2008/0163631 A1, published Jul. 10, 2008, entitled “METHODSFOR CONFIGURING TUBING FOR INTERCONNECTING IN-SERIES MULTIPLELIQUID-COOLED COLD PLATES”, assigned to the same assignee as the presentapplication. While this option allows for mechanically independentattach solutions for each coldplate/component (or module) combinationand allows each coldplate to have a relatively small mass, it greatlyincreases the risk of leaking, given the large number of flexible tubeinterconnects. The risk of leaking is amplified when the burst strengthof the flexible tube interconnects is sacrificed to achieve theflexibility required to route the flexible tube interconnects.

High performance computer systems may also employ a combination of afixed-gap coldplate and an articulated coldplate. Typically, thefixed-gap coldplate is positioned over electronic components havingrelatively low power dissipation, and the articulated coldplate ispositioned over one or more high power processor components. Thesecoldplates are interconnected with flexible tubing, such as coppertubing with a free-expansion loop. Such a scheme is disclosed in U.S.Patent Application Publication 2009/0213541 A1, published Aug. 27, 2009,entitled “COOLING PLATE ASSEMBLY WITH FIXED AND ARTICULATED INTERFACES,AND METHOD FOR PRODUCING SAME”, assigned to the same assignee as thepresent application. This option allows a minimal number of flexibletube interconnects and thereby decreases the risk of leaking (ascompared to solutions that require a large number of flexible tubeinterconnects). Unfortunately, the risk of leaking nonetheless remainswhen the burst strength of the flexible tube interconnects is sacrificedto achieve the flexibility required to route the flexible tubeinterconnects.

The choice of material for making the flexible tube interconnectspresents a challenge with respect to ensuring adequate reliability. Thetubing material must satisfy two requirements that are in conflict withone another: flexibility (determined as the minimum bend radius prior tokinking) and burst strength. In order to achieve the flexibilityrequired to route the tubing through the CEC, the burst strength isoften sacrificed (e.g., the tubing wall strength is reduced). It isdesirable to be able to maintain tubing flexibility without sacrificingburst strength.

Therefore, a need exists for an enhanced tubing material for use incooling plate assemblies and other applications.

SUMMARY OF THE INVENTION

According to the preferred embodiments of the present invention, acooling plate assembly for transferring heat from electronic componentsmounted on a circuit board includes a flexible-to-rigid tube throughwhich coolant flows. The flexible-to-rigid tube is flexible when routedand is then rigidized to increase burst strength. In one embodiment, theflexible-to-rigid tube (while in a flexible state) includes apolydimethylsiloxane (PDMS) or other silicone containing pendant orterminal epoxy, vinyl and/or acrylate functional groups and an initiator(e.g., a sulfonium salt photoinitiator, a free radical photoinitiator,or a thermal initiator). In another embodiment, triallyl isocyanurate(TAIC) and an initiator are incorporated into a conventional PVC-basedtubing material. The flexible-to-rigid tube changes from a flexiblestate to a rigid state via formation of a cross-linked network uponexposure to actinic radiation or heat. The flexible-to-rigid tube may beused in cooling plate assemblies and other applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred exemplary embodiments of the present invention willhereinafter be described in conjunction with the appended drawings,where like designations denote like elements.

FIG. 1 is a top plan view of a cooling plate assembly havingflexible-to-rigid tubing according to the preferred embodiments of thepresent invention.

FIG. 2 is a top plan view of a cooling plate assembly having a fixed-gapcooling plate and an articulated cooling plate interconnected withflexible-to-rigid tubing and in fluid communication with a reservoircontaining cooling fluid according to the preferred embodiments of thepresent invention.

FIG. 3 is cross-sectional view of a flexible-to-rigid tube embodiment ofthe present invention.

FIG. 4 is cross-sectional view of a multi-layer flexible-to-rigid tubeembodiment of the present invention.

FIG. 5 is a flow diagram of a method for installing flexible-to-rigidtubing according to the preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1. Overview

In accordance with the preferred embodiments of the present invention, acooling plate assembly for transferring heat from electronic componentsmounted on a circuit board includes a flexible-to-rigid tube throughwhich coolant flows. The flexible-to-rigid tube is flexible when routedand is then rigidized to increase burst strength. In one embodiment, theflexible-to-rigid tube (while in a flexible state) includes apolydimethylsiloxane (PDMS) or other silicone containing pendant orterminal epoxy, vinyl and/or acrylate functional groups and an initiator(e.g., a sulfonium salt photoinitiator, a free radical photoinitiator,or a thermal initiator). In another embodiment, triallyl isocyanurate(TAIC) and an initiator are incorporated into a conventional PVC-basedtubing material. The flexible-to-rigid tube changes from a flexiblestate to a rigid state via formation of a cross-linked network uponexposure to actinic radiation or heat. The flexible-to-rigid tube may beused in cooling plate assemblies and other applications.

2. Detailed Description

Referring now to FIG. 1, there is depicted, in a top plan view, acooling plate assembly 100 that utilizes one or more flexible-to-rigidtubes 162 and 164 in accordance with the preferred embodiments of thepresent invention. In the embodiment shown in FIG. 1, theflexible-to-rigid tubes 162 and 164 interconnect a fixed-gap coolingplate 102 (also referred to herein as a “fixed-gap coldplate”) and anarticulated cooling plate 104 (also referred to herein as an“articulated coldplate” or a “floating coldplate”). The embodiment shownin FIG. 1 employs a combination of a fixed-gap coldplate and anarticulated coldplate. This particular type of cooling plate assembly isshown in FIG. 1 for the purpose of illustrating an exemplary applicationof the present invention. One skilled in the art will appreciate that aflexible-to-rigid tube in accordance with the present invention may beutilized in other cooling plate assemblies (e.g., a cooling plateassembly employing multiple articulated-gap cold plates) and otherapplications (e.g., re-piping in residential and commercial buildings).

With the exception of the flexible-to-rigid tubes 162 and 164, thecooling plate assembly 100 shown in FIG. 1 is conventional.Specifically, the cooling plate assembly 100 is a modified-version ofthe cooling plate assembly disclosed in U.S. Patent ApplicationPublication 2009/0213541 A1, published Aug. 27, 2009, entitled “COOLINGPLATE ASSEMBLY WITH FIXED AND ARTICULATED INTERFACES, AND METHOD FORPRODUCING SAME”, assigned to the same assignee as the presentapplication, and hereby incorporated herein by reference in itsentirety. In the prior art, the flexible tubes used to interconnect thefixed-gap coldplate and the articulated coldplate are typically made ofa high thermal conductivity material, such as copper, aluminum,stainless steel, or other metal. Such conventional flexible tubes areeach typically fabricated from low modulus metal tubing (e.g., 5-10 mmdiameter copper tubing) that is bent to form a free-expansion loop. Thefree-expansion loop increases the length of the tube and therebyenhances the tube's flexibility as compared to a shorter, more directlyrouted tube. The free-expansion loop enhances the ability of the tube toaccommodate relative movement between the cooling plates (e.g., duringattachment of the cooling plates to the printed circuit board) whileimparting a relatively low reaction force in response to that relativemovement. Typically, brazing is utilized in connecting the conventionalflexible tubes to the cooling plates. Unfortunately, the cost of suchconventional flexible tubes can be prohibitive in light of the expenseof the metal material, the metal bending process used to form thefree-expansion loop, and the brazing process used for connection.

Another solution is to achieve the requisite flexibility by reducing thetubing wall strength (e.g., using a polymer tubing material rather thana metal tubing material). Heretofore, this solution achieved therequisite flexibility but only at the expense of sacrificing burststrength. Flexible-to-rigid tubing in accordance to the presentinvention solves this problem. Flexible-to-rigid tubing is flexible whenrouted and is then rigidized to increase burst strength. Also,flexible-to-rigid tubing is less expensive to implement because it doesrequires neither a metal bending process nor a brazing process forconnection.

The transition from flexible to rigid tubing is accomplished bycrosslinking the base polymer after the tubing has been routed throughthe CEC. Crosslinking is accomplished by use of pendant and/or terminalgroups off the main polymer chain which can be crosslinked via variouschemistry approaches.

The flexibility of tubing is typically measured as the minimum bendradius prior to kinking. For example, an exemplary flexible-to-rigidtube having an outside diameter (O.D.) of ¼ inch and a wall thickness of1/16 inch, may have a flexibility (minimum bend radius) of 1 inch in itsflexible state. The burst strength of tubing is typically measured as amaximum working pressure at a given temperature. For example, theexemplary flexible-to-rigid tube having an outside diameter (O.D.) of ¼inch and a wall thickness of 1/16 inch, may have a burst strength(maximum working pressure) of 60 PSI at 160° F. in its rigid state (and40 PSI at 160° F. in its flexible state). The particular parametervalues set forth in this example are for purposes of illustration, notlimitation.

In the embodiment illustrated in FIG. 1, the fixed-gap cooling plate 102is “fixedly” mounted to a printed circuit board (PCB) 106 using arelatively thick compliant thermal interface material, while thearticulated cooling plate 104 is gimbal-mounted to the PCB 106 using arelatively high performance interface with low thickness and highcontact pressure provided by a spring loading mechanism. One or moreelectronic components to be cooled by the fixed-gap cooling plate 102is/are mounted on the top surface 107 of the PCB 106, as is one or moreelectronic components to be cooled by the articulated cooling plate 104.

In the embodiment shown in FIG. 1, the fixed-gap cooling plate 102provides cooling for electronic components 110, 112, 114, 116 and 118(shown as phantom lines in FIG. 1), which may be lower power components,such as low power processors, field programmable gate arrays (FPGAs),memory arrays, modules with one or more chips, and the like. In theembodiment shown in FIG. 1, the fixed-gap cooling plate 102 has agenerally U-shaped configuration that includes two leg portions 120, 122each extending from a base portion 124. One skilled in the art willappreciate that the configuration of the fixed-gap cooling plate 102shown in FIG. 1 is exemplary and that a fixed-gap cooling plate may beconfigured to have any shape. Likewise, a fixed-gap cooling plate mayprovide cooling for any number and any type of electronic components.Typically, the electronic components cooled by the fixed-gap coolingplate 102 have relatively low power dissipation as compared to therelatively high power dissipation of the one or more electroniccomponents cooled by the articulated cooling plate 104, i.e., electroniccomponent 130.

The electronic components cooled by the fixed-gap cooling plate 102 aretypically in thermal contact with the fixed-gap cooling plate 102through a compressive pad thermal interface material (TIM) (not shown).The compressive pad TIM may be a re-usable elastomerically conformabletype, or it may be pre-cured or, alternatively, may be cured in-situ.For example, the compressive pad TIM may be provided by mixing amulti-part liquid material and then applying the mixture to thefixed-gap cooling plate 102 and/or the electronic components. An exampleof a suitable composition for the compressive pad TIM is a fiberglassreinforced, thermally conductive silicone gel pad (commerciallyavailable from Dow Corning Corporation, Midland, Mich.).

In the embodiment shown in FIG. 1, the articulated cooling plate 104 hasa substantially rectangular configuration and is substantiallysurrounded by the fixed-gap cooling plate 102. That is, the articulatedcooling plate 104 is positioned between the leg portions 120, 122 of thefixed-gap cooling plate 102 and adjacent the base portion 124 of thefixed-gap cooling plate 102. One skilled in the art will appreciate thatthe configuration of the articulated cooling plate 104 is exemplary, asis the positioning of the articulated cooling plate 104 relative to thefixed-gap cooling plate 102, and that an articulated cooling plate maybe configured to have any shape and position relative to the fixed-gapcooling plate. The articulated cooling plate 104 typically providescooling for a high power electronic component 130 (shown as phantomlines in FIG. 1), which is typically a high power processor, a modulewith one or more high power processor chips, and the like having arelatively high power dissipation. One skilled in the art willappreciate that an articulated cooling plate may provide cooling for anynumber and any type of electronic components.

In the embodiment shown in FIG. 1, a single coolant channel connects thefixed-gap cooling plate to the articulated cooling plate. In theembodiment shown in FIG. 1, the fixed-gap cooling plate 104 includesthermal dissipation channels 140 and 142, while the articulated coolingplate 106 includes a thermal dissipation channel 144. The thermaldissipation channel 140 extends through a lower-side (as viewed inFIG. 1) of the fixed-gap cooling plate 102 from an inlet port 150 at thebase portion 124 to an outlet port 152 at the leg portion 120. Thethermal dissipation channel 142 extends through an upper-side (as viewedin FIG. 1) of the fixed-gap cooling plate 102 from an inlet port 154 atthe leg portion 122 to an outlet port 156 at the base portion 124. Thethermal dissipation channel 144 extends through the articulated coolingplate 104 from an inlet port 158 to an outlet port 160.

In the embodiment shown in FIG. 1, a flexible-to-rigid tube 162interconnects the outlet port 152 of the thermal dissipation channel 140of the fixed-gap cooling plate 102 to the inlet port 158 of the thermaldissipation channel 144 of the articulated cooling plate 104. Similarly,a flexible-to-rigid tube 164 interconnects the outlet port 160 of thethermal dissipation channel 144 of the articulated cooling plate 104 tothe inlet port 154 of the thermal dissipation channel 142 of thefixed-gap cooling plate 102. In accordance with the preferredembodiments of the present invention, the flexible-to-rigid tubes 162and 164 are routed while in a flexible state and are then “rigidized” toincrease burst strength. The flexible-to-rigid tubes 162 and 164, whilein the flexible state, are sufficiently flexible to allow the tubes tobe readily routed between and connected to the input and output ports ofthe cooling plates 102 and 104. Preferably, the flexible-to-rigid tubes162 and 164 are changed from the flexible state to the rigid state viaformation of a cross-linked network upon exposure of theflexible-to-rigid tubes 162 and 164 to actinic radiation or heat.

The flexible-to-rigid tubes 162 and 164, in accordance with thepreferred embodiments of the present invention, include at least onerigidizable material. In one embodiment, described below with referenceto FIG. 3, the flexible-to-rigid tubes 162 and 164 include apolydimethylsiloxane (PDMS) and a sulfonium salt catalyst. In anotherembodiment, described below with reference to FIG. 4, theflexible-to-rigid tubes 162 and 164 include triallyl isocyanurate (TAIC)and an initiator (e.g., a free radical photoinitiator or a thermalinitiator) incorporated into a PVC-based tubing material. Theflexible-to-rigid tubes 162 and 164 change from a flexible state to arigid state via formation of a cross-linked network upon exposure toactinic radiation or heat.

In the embodiment shown in FIG. 1, the flexible-to-rigid tubes 162 and164 are routed to form a free-expansion loop. The free-expansion loopincreases the length of the tube and thereby enhances the tube'sflexibility as compared to a shorter, more directly routed tube. Thefree-expansion loop enhances the ability of the tube to accommodaterelative movement between the cooling plates while imparting arelatively low reaction force in response to that relative movement.

The flexible-to-rigid tubes 162 and 164 typically have an outer diameterof 5-10 mm and a wall thickness of 1-2 mm, but may have any suitableoutside diameter and wall thickness.

The flexible-to-rigid tubes 162 and 164 may be connected to thefixed-gap cooling plate 102 and the articulated cooling plate 104 usingany suitable conventional fastening technique. For example, conventionalbarbed insert fittings may be used. Single barb insert fittings, forinstance, have a land behind the barb that allows a clamp to be fastenedover the tubing. In any event, the fastening technique preferably alsoserves to effectively seal the tubes relative to the cooling plates toprevent coolant leaks.

The single barb insert fitting is an example of a suitable conventionalfastening technique that may be utilized in connecting theflexible-to-rigid tubes to the cooling plates. For example, four singlebarb insert fittings (not shown) may be inserted and sealed into theoutlet port 152 of the fixed-gap cooling plate 102, the inlet port 158of the articulated cooling plate 104, the outlet port 160 of thearticulated cooling plate 104, and the inlet port 154 of the fixed-gapcooling plate 102 using conventional techniques. Then, the ends of theflexible-to-rigid tube 162 may be slid over and in turn clamped to(e.g., by tightening a clamp over each end of the tube) two single barbinsert fittings respectively provided on the outlet port 152 of thethermal dissipation channel 140 of the fixed-gap cooling plate 102 andthe inlet port 158 of the thermal dissipation channel 144 of thearticulated cooling plate 104. Similarly, the ends of theflexible-to-rigid tube 164 may be slid over and in turn clamped to(e.g., by tightening a clamp over each end of the tube) two single barbinsert fittings respectively provided on the outlet port 160 of thethermal dissipation channel 144 of the articulated cooling plate 104 andthe inlet port 154 of the thermal dissipation channel 142 of thefixed-gap cooling plate 102.

Typically, the fixed-gap cooling plate 102 and the articulated coolingplate 104 are made of a high thermal conductivity material, such ascopper, aluminum, stainless steel, or other metal. In some embodiments,the fixed-cooling plate 102 and/or the articulated cooling plate 104 maybe made of silicon (e.g., single-crystal silicon or polycrystallinesilicon) to match the coefficient of thermal expansion of the siliconchips being cooled.

The fixed-gap cooling plate 102 and the articulated cooling plate 104may have a multi-part construction to facilitate the formation of thethermal dissipation channels 140, 142 and 144. For example, each of thecooling plates may be constructed by joining a top plate to a bottomplate, at least one of which has at least a portion of one or morethermal dissipation channels formed on a surface thereof at theinterface between top plate and the bottom plate. The top plate and thebottom plate may be joined together using any suitable conventionalfastening technique such as brazing, soldering, diffusion bonding,adhesive bonding, etc. For example the top plate may be bonded to thebottom plate using a silver filled epoxy, filled polymer adhesive,filled thermoplastic or solder, or other thermally conductive bondingmaterial. The fastening technique preferably also serves to effectivelyseal the plates together to prevent coolant leaks.

The thermal dissipation channels may be formed on the surface of eitheror both the top plate and the bottom plate by any suitable conventionaltechnique such as routing, sawing or other milling technique, or byetching.

In lieu of a multi-part construction, the fixed-gap cooling plate 102and/or the articulated cooling plate 104 may have a one-piececonstruction. For example, the thermal dissipation channels may beformed in the fixed-gap cooling plate 102 and/or the articulated coolingplate 104 through a milling operation (e.g., drilling).

FIG. 2 is a top plan view of a cooling plate assembly 100 having afixed-gap cooling plate 102 and an articulated cooling plate 104interconnected with flexible-to-rigid tubing 162 and 164 and in fluidcommunication with a reservoir 210 containing cooling fluid according tothe preferred embodiments of the present invention. A cooling fluid ispreferably pumped from thermal reservoir 210 through a supply conduit212 to inlet port 150 of the cooling plate assembly 100, where thecooling fluid picks up heat as it travels through thermal dissipationchannels of the fixed-gap cooling plate 102 and the articulated coolingplate 104. Then, the cooling fluid is exhausted from outlet port 156 ofthe cooling plate assembly 100 through an exhaust conduit 214 andreturns to thermal reservoir 210. A pump 216 is preferably provided toforce the cooling fluid through the recirculation loop. Prior torecirculating the cooling fluid through the recirculation loop, it maybe desirable to cool the cooling fluid. For example, the cooling fluidmay be cooled in the reservoir or elsewhere using a heat exchanger,waterfall, radiator, or other conventional cooling mechanism. Thecooling fluid may be any suitable coolant, for example, an inertperfluorocarbon fluid, such as 3M Fluorinert™ commercially availablefrom 3M Company, St. Paul, Minn. Other suitable coolants include, butare not limited to, water, ethylene glycol, ethylene glycol/watermixture, polyalphaolefin (PAO), ammonia, methanol, nitrogen, and thelike.

Supply conduit 212 and exhaust conduit 214 are respectively attached toinlet port 150 and outlet port 156 of the cooling plates assembly 100using any suitable conventional fastening technique, such as byinserting and sealing tubular fittings into inlet port 150 and outletport 156, and then mating supply conduit 212 and exhaust conduit 214over the tubular fittings to provide a tight seal. Supply conduit 212and exhaust conduit 214 may be rubber, metal or some other suitablematerial that is compatible with the coolant. The supply conduit 212and/or the exhaust conduit 214 may be flexible-to-rigid tubing.

In general, the rate of heat transfer can be controlled by using variousthermal transport media in the internal structure of the cooling plateassembly 100. For example, the rate of heat transfer can be controlledby varying the composition and/or the flow rate of the cooling fluid.Also, the rate of heat transfer is a function of the configuration ofthe thermal dissipation channels within the cooling plate assembly 100.

FIG. 3 is cross-sectional view of a flexible-to-rigid tube 300 accordingto an embodiment of the present invention. The flexible-to-rigid tube300 shown in FIG. 3 may correspond to one or more of theflexible-to-rigid tubes 162 and 164 shown in FIGS. 1 and 2. In theembodiment illustrated in FIG. 3, the flexible-to-rigid tube 300 issilicone based. Silicone tubing is an industry standard flexible tubing,often with a minimum bend radius less than 0.5 inch. Unfortunately, toachieve such flexibility, the burst strength of conventional siliconetubing is typically marginal. Conventional silicone tubing typicallycomprises polydimethylsiloxane (PDMS). Accordingly, PDMS is used in theembodiment illustrated in FIG. 3. However, one skilled in the art willappreciate that other silicones may be used in accordance with thepresent invention and that this embodiment is not limiting. Numerousexamples of silicone (PDMS and non-PDMS) chains containing pendant orterminal epoxy, vinyl and acrylate functional groups are described in“Reactive Silicones: Forging New Polymer Links”, Gelest, Inc.,Morrisville, Pa., Mar. 25, 2009, which is hereby incorporated herein byreference in its entirety.

PDMS has the chemical formula CH₃[Si(CH₃)₂O]_(n)Si(CH₃)₃, where n is thenumber of repeating monomer [Si(CH₃)₂O] units. The chemical structure ofPDMS is shown below.

PDMS belongs to a group of polymeric organosilicon compounds (i.e.,organic compounds containing carbon silicon bonds) that are commonlyreferred to as silicones (also referred to as polymerized siloxanes orpolysiloxanes). As illustrated in FIG. 3, in its flexible state, theflexible-to-rigid tube 300 includes a single layer 302 incorporatingPDMS (having at least one pendant or terminal crosslinkable group) andan initiator (e.g., a photoinitiator).

By incorporating either a pendant crosslinkable group in the PDMS chain(e.g., epoxycyclohexylethylmethylsiloxane)-dimethylsiloxane copolymer asillustrated in FIG. 3) of layer 302, along with a sulfonium saltcatalyst (e.g., triphenylsulfonium triflate as illustrated in FIG. 3) orany other suitable photoinitiator (e.g., an onium photoinitiator), thePDMS can be crosslinked upon exposure to actinic radiation. Uponcrosslinking, the flexural modulus of the flexible-to-rigid tubing willincrease as will the burst strength (maximum working pressure). Thereaction for the silicone-based embodiment illustrated in FIG. 3 is setforth in Reaction 1 below. The constituent reactants in Reaction 1,i.e., (epoxycyclohexylethylmethylsiloxane)-dimethylsiloxane copolymerand triphenylsulfonium triflate, are commercially available.

For the sake of clarity, the R group in the Reaction 1 represents thePDMS backbone. The extent of crosslinking illustrated in Reaction 1 isexemplary. As illustrated in Reaction 1, three of the PDMS chains arecrosslinked. However, one skilled in the art will appreciate that anysuitable extent of crosslinking may be utilized in accordance with thepresent invention. The extent of crosslinking is a significant factor inthe flexural modulus of the flexible-to-rigid tube in the rigid state.

The flexible-to-rigid tubing 300 is routed into place while still in theflexible state. UV light from a conventional portable UV light source,for example, is then used to expose the flexible-to-rigid tubing 300.Exposure to the UV light “rigidizes” the flexible-to-rigid tubing 300(i.e., increases the flexural modulus of the flexible-to-rigid tubing300) and increases its burst strength. Upon exposure, thetriphenylsulfonium salt liberates acid (H+) via well establishedchemistry. The pendant cyclohexylepoxy rapidly reacts with the protonvia cationic ring-opening polymerization to result in a crosslinkednetwork. Depending on the desired flexural modulus, the concentration ofpendant epoxy groups and photoinitiator can be tailored to the specificapplication.

The silicone-based embodiment illustrated in FIG. 3 is exemplary. Manyvariations are possible. For example, one skilled in the art willappreciate that a terminal crosslinkable group may be incorporated inthe PDMS chain (e.g., 3-glycidoxypropyl terminated PDMS) in lieu of, orin addition to, a terminal crosslinkable group as shown in FIG. 3. Thechemical structure of an exemplary commercially available3-glycidoxypropyl terminated PDMS suitable for use in the presentinvention is shown below.

Additionally, PDMS chains containing pendant or terminal functionalgroups such as vinyl and acrylate groups can be used to produce aflexible-to-rigid tube in accordance with the present invention, in aprocess similar to that described above for PDMS chains containingpendent epoxies. However, the sulfonium salt photoinitiator used inReaction 1 would be replaced by a free radical photoinitiator such asbenzoin, or a thermal initiator such as azobisisobutyronitrile orbenzoyl peroxides (e.g., dibenzoylperoxide andbis(dichlorobenzoyl)peroxide).

Commercially available examples of PDMS chains containing pendant orterminal vinyl and acrylate functional groups abound. Examples suitablefor use in the present invention are set forth below, but one skilled inthe art will appreciate that other PDMS chains and other silicone chainscontaining pendant or terminal vinyl and acrylate functional groups maybe used and that the examples set forth are not limiting. Numerousexamples of silicone (PDMS and non-PDMS) chains containing pendant orterminal vinyl and acrylate functional groups (e.g., vinyl Q resins andvinyl T resins) are described in “Reactive Silicones: Forging NewPolymer Links”, Gelest, Inc., Morrisville, Pa., Mar. 25, 2009, which isincorporated herein by reference in its entirety. The chemical structureof an exemplary commercially available vinyl terminated PDMS and anexemplary commercially available vinyl terminated diphenylsiloxane-PDMScopolymer suitable for use in the present invention are shown below, aswell as an exemplary commercially available vinylmethylsiloxane-PDMScopolymer with pendant vinyl group.

The chemical structure of methacrylate and acrylate functional siloxanes(generic structure) suitable for use in the present invention is shownbelow, as well as an exemplary commercially available(methacryloxypropyl)methylsiloxane-PDMS copolymer with a pendantmethacrylate group.

While PDMS is the most common polysiloxane, silicone based embodimentsof the present invention are not limited thereto. As mentioned earlier,other silicone chains containing pendant or terminal vinyl and acrylatefunctional groups may be used in the present invention. Examples of suchsilicones are vinyl Q resins and vinyl T resins. Vinyl Q resins aretypically clear reinforcing additives for addition cure elastomers.Vinyl T resins are T-structure polymers (i.e., contain multiple branchpoints) that have a vinyl branch point and/or a vinyl branch terminus.(T resins contain silicon species which contain three oxygens and an Rgroup. Q resins contain a silicon species which contains four oxygens.Not every silicon species in the resin contains that formula but amajority does.) The chemical structure of an exemplary commerciallyavailable vinyl Q resin suitable for use in the present invention isshown below, as well as an exemplary commercially available vinyl Tresin having a vinyl branch point and an exemplary commerciallyavailable vinyl T resin having a vinyl branch terminus.

The burst strength of the tubing could be even further increased throughthe addition of triallyl isocyanurate (TAIC), a common hardener used inlaminate manufacturing of printed circuit boards. The chemical structureof TAIC is shown in Reaction 2, below. In this case, once the tubing isrouted into place, the assembly would be subjected to elevatedtemperature selected based upon the free radical half life.Polymerization of the flexible-to-rigid tubing ensues and the flexuralmodulus and burst strength dramatically increases.

Another embodiment of the present invention involves modification ofconventional flexible tubing, such as compounded PVC tubing, toincorporate TAIC and an initiator. The most common form of flexibletubing is compounded PVC tubing because it imparts chemical resistanceand flexibility. Compounded PVC tubing is available from, for example,Saint-Gobain Performance Plastics, Akron, Ohio under the tradenameTYGON® Inert Tubing. Incorporation of TAIC/initiator into the compoundedPVC in accordance with the present invention results in a PVC-basedtubing material that can be “rigidized” by heat (or thermal energy).

FIG. 4 is cross-sectional view of a multi-layer flexible-to-rigid tube400 according to another embodiment of the present invention. Themulti-layer flexible-to-rigid tube 400 shown in FIG. 4 may correspond toone or more of the flexible-to-rigid tubes 162 and 164 shown in FIGS. 1and 2. In the embodiment illustrated in FIG. 4, the multi-layerflexible-to-rigid tube 400 is PVC based. The multi-layerflexible-to-rigid tube 400 has a crosslinkable, compounded PVC jacket402 extruded over a conventional, compounded PVC inner liner 404. Inaccordance with this embodiment of the present invention, conventionalmulti-layer tubing is modified to incorporate triallyl isocyanurate(TAIC) and an initiator into the compounded PVC jacket 402. For example,the multi-layer flexible-to-rigid tube 400 may be a modified version ofTYGON® Formulation SE-200 Inert Tubing, available from Saint-GobainPerformance Plastics, Akron, Ohio, which is modified in accordance withthe present invention to incorporate TAIC and an initiator into thecompounded PVC jacket.

The multi-layer flexible-to-rigid tube 400 is formed by extruding thecrosslinkable, compounded PVC jacket 402 material over the conventional,compounded PVC inner liner 404. The extrusion process is conventional.Because the crosslinkable, compounded PVC jacket 402 is essentiallyidentical to the conventional, compounded PVC inner liner 404, theflexibility of the tubing is retained. The TAIC/initiator concentrationcan be tailored at will, but 10 wt % will provide a noticeable increasein burst pressure. Preferably, the initiator is a free radicalphotoinitiator such as benzoin, or a thermal initiator such asazobisisobutyronitrile or benzoyl peroxides (e.g., dibenzoylperoxide andbis(dichlorobenzoyl)peroxide). Because TAIC is a liquid monomer, evengreater concentrations will not degrade the flexibility. Once themulti-layer flexible-to-rigid tube 400 is positioned as desired, eitherUV or thermal energy (depending on the type of initiator selected)crosslinks the TAIC into a hard, intractable resin thereby increasingthe modulus and burst strength.

The reaction for the PVC-based embodiment illustrated in FIG. 4 is setforth in Reaction 2 below. The constituent reactants in Reaction 2,i.e., TAIC and dibenzoylperoxide (i.e., the exemplary initiator selectedin this embodiment), are commercially available. Other suitableinitiators for use with TAIC include, but are not limited to, Micheler'sketone or any number of the various Ciba® IRGACURE® photoinitiators(available from Ciba Specialty Chemicals, Basel, Switzerland, now partof BASF), which crosslink the TAIC in the crosslinkable, compounded PVCjacket 402 upon exposure to actinic radiation.

In Reaction 2, the extent of cros slinking is represented by n. Oneskilled in the art will appreciate that any suitable extent ofcrosslinking may be utilized in accordance with the present invention.The extent of crosslinking is a significant factor in the flexuralmodulus of the multi-layer flexible-to-rigid tube 400 in the rigidstate.

FIG. 5 is a flow diagram of a method 500 for installingflexible-to-rigid tubing according to the preferred embodiments of thepresent invention. The method 500 sets forth the preferred order of thesteps. It must be understood, however, that the various steps may occurat any time relative to one another. A circuit board is provided onwhich electronic components are mounted (step 510). This step isconventional. For example, the circuit board referred to in method 500may be the PCB 106 (FIG. 1), on which are mounted a high powerelectronic component 130 and low power electronic components 110, 112,114, 116 and 118. This step is conventional.

A first cooling plate having a thermal dissipation channel extendingthrough a portion thereof is positioned over and in thermal contact withat least one electronic component mounted on the circuit board (step520). For example, the first cooling plate referred to in method 500 maybe the fixed-gap cooling plate 102 (FIG. 1), through which extendthermal dissipation channels 140 and 142. In this case, step 520 isperformed by attaching the fixed-gap cooling plate 102 over and inthermal contact with the low power electronic components 110, 112, 114,116 and 118 mounted on a top surface of the PCB 106. Step 520 may alsoinclude interposing a compressive pad TIM between the fixed-gap coolingplate 102 and the low power electronic components 110, 112, 114, 116 and118. This step is conventional.

A second cooling plate having a thermal dissipation channel extendingthrough a portion thereof is positioned over and in thermal contact withat least one electronic component mounted on the circuit board (step530). For example, the second cooling plate referred to in method 500may be the articulated cooling plate 104 (FIG. 1), through which extendsthermal dissipation channel 144. In this case, step 530 is performed byattaching the articulated cooling plate 102 over and in thermal contactwith the high power electronic component 130 mounted on a top surface ofthe PCB 106. Step 530 may also include actuating a mechanical attachsystem, such as a conventional post/spring-plate type clampingmechanism, to provide a spring-loading force that biases the articulatedcooling plate 104 in thermal contact with the high power electroniccomponent 130. This step is conventional.

The method 500 continues by interconnecting the thermal dissipationchannel of the first cooling plate and the thermal dissipation channelof the second cooling plate using a flexible-to-rigid tube (step 540).Step 540 includes routing the flexible-to-rigid tube in a flexible statebetween the thermal dissipation channel of the first cooling plate andthe thermal dissipation channel of the second cooling plate.

For example, the flexible-to-rigid tube referred to in method 500 may bethe flexible-to-rigid tubing 162 and 164 (FIG. 1). The flexible-to-rigidtubing 162 and 164 may be connected to the fixed-gap cooling plate 102and the articulated cooling plate 104 using any suitable conventionalfastening technique. For example, conventional single barb insertfittings may be utilized in connecting the flexible-to-rigid tubing 162and 164 to the cooling plates 102 and 104. If conventional single barbinsert fittings are used, the cooling plate 102 would include two singlebarb insert fittings respectively inserted and sealed into the outletport 152 and the inlet port 154. Similarly, the articulated coolingplate 104 would include two single barb insert fittings respectivelyinserted and sealed into the inlet port 158 and the outlet port 160.

In one embodiment, the flexible-to-rigid tube (while in a flexiblestate) includes a polydimethylsiloxane (PDMS) or other siliconecontaining pendant or terminal epoxy, vinyl and/or acrylate functionalgroups and an initiator (e.g., a sulfonium salt photoinitiator, a freeradical photoinitiator, or a thermal initiator). In another embodiment,triallyl isocyanurate (TAIC) and an initiator are incorporated into aconventional PVC-based tubing material.

During step 540, the ends of the flexible-to-rigid tube 162 may be slidover and in turn clamped to (e.g., by tightening a clamp over each endof the tube) two single barb insert fittings respectively provided onthe outlet port 152 of the thermal dissipation channel 140 of thefixed-gap cooling plate 102 and the inlet port 158 of the thermaldissipation channel 144 of the articulated cooling plate 104. Alsoduring step 540, the ends of the flexible-to-rigid tube 164 may be slidover and in turn clamped to (e.g., by tightening a clamp over each endof the tube) two single barb insert fittings respectively provided onthe outlet port 160 of the thermal dissipation channel 144 of thearticulated cooling plate 104 and the inlet port 154 of the thermaldissipation channel 142 of the fixed-gap cooling plate 102.

Next, the method 500 continues by rigidizing the flexible-to-rigid tube(step 550). Step 550 is accomplished through the formation of across-linked network to change the flexible-to-rigid tubing 162 and 164from the flexible state to a rigid state upon exposure to actinicradiation or heat (depending on the type of initiator selected). Forexample, UV light from a conventional portable UV light source may beused to expose the flexible-to-rigid tubing 162 and 164. In thisexample, exposure to the UV light “rigidizes” the flexible-to-rigidtubing 162 and 164 (i.e., increases the flexural modulus of theflexible-to-rigid tubing 162 and 164) and increases its burst strength.

In an alternative example, thermal energy (e.g., absorbed from a fluidpumped through the tubing, preferably at low pressure) may be used toexpose the flexible-to-rigid tubing 162 and 164. In this alternativeexample, exposure to the thermal energy “rigidizes” theflexible-to-rigid tubing 162 and 164 (i.e., increases the flexuralmodulus of the flexible-to-rigid tubing 162 and 164) and increases itsburst strength.

One skilled in the art will appreciate that many variations are possiblewithin the scope of the present invention. For example, theflexible-to-rigid tubing in accordance with the present invention may beutilized in applications beyond cooling plate assemblies in industriessuch as: the automotive industry (for applications such asinterconnecting components for engine cooling); the food and beverageindustry (for applications such as beverage dispensing/vending); and thebuilding industry (for applications such as re-piping in residential andcommercial buildings). Thus, while the present invention has beenparticularly shown and described with reference to the preferredembodiments thereof, it will be understood by those skilled in the artthat these and other changes in form and detail may be made thereinwithout departing from the spirit and scope of the present invention.

What is claimed is:
 1. A cooling plate assembly for transferring heatfrom a plurality of electronic components mounted on a circuit board,comprising: a circuit board having a top surface and a bottom surface; afirst cooling plate positioned over and in thermal contact with at leastone electronic component mounted on the top surface of the circuit boardand having a thermal dissipation channel extending through a portionthereof; a second cooling plate positioned over and in thermal contactwith at least one electronic component mounted on the top surface of thecircuit board and having a thermal dissipation channel extending througha portion thereof; a flexible-to-rigid tube interconnecting the thermaldissipation channel of the first cooling plate and the thermaldissipation channel of the second cooling plate, wherein theflexible-to-rigid tube comprises a cross-linked network that includes atleast one of a silicone or triallyl isocyanurate (TAIC).
 2. The coolingplate assembly as recited in claim 1, wherein the cross-linked networkis a polymerization reaction product of: a polydimethylsiloxane (PDMS)having a pendant or terminal functional group selected from a group offunctional groups consisting of epoxy functional groups, vinylfunctional groups, and acrylate functional groups; and an initiator. 3.The cooling plate assembly as recited in claim 2, wherein the PDMS has apendant or terminal epoxy functional group, wherein the initiator is anonium photoinitiator, and wherein the polymerization reaction occursupon exposure of the flexible-to-rigid tube to actinic radiation.
 4. Thecooling plate assembly as recited in claim 1, wherein the cross-linkednetwork is a polymerization reaction product of: triallyl isocyanurate(TAIC); and an initiator selected from a group of initiators consistingof free radical photoinitiators and thermal initiators.
 5. The coolingplate assembly as recited in claim 4, wherein the initiator comprises afree radical photoinitiator including benzoin, and wherein thepolymerization reaction occurs upon exposure of the flexible-to-rigidtube to actinic radiation.
 6. The cooling plate assembly as recited inclaim 4, wherein the initiator comprises a thermal initiator including abenzoyl peroxide or azobisisobutyronitrile, and wherein thepolymerization reaction occurs upon exposure of the flexible-to-rigidtube to heat.
 7. The cooling plate assembly as recited in claim 4,wherein the TAIC and the initiator are incorporated into a PVC-basedtubing material.
 8. The cooling plate assembly as recited in claim 1,wherein the thermal dissipation channels of the first cooling plate andthe second cooling plate are in fluid communication with a reservoircontaining cooling fluid, and wherein the flexible-to-rigid tubecomprises at least one of: a flexible-to-rigid tube interconnecting anoutlet port of the first cooling plate and an inlet port of the secondcooling plate; and a flexible-to-rigid tube interconnecting an outletport of the second cooling plate and an inlet port of the first coolingplate.
 9. A flexible-to-rigid tube, comprising: a layer having acomposition comprising at least one of a silicone and triallylisocyanurate (TAIC), wherein the layer changes from a flexible state toa rigid state via formation of a cross-linked network upon exposure ofthe layer to actinic radiation or heat.
 10. The flexible-to-rigid tubeas recited in claim 9, wherein the cross-linked network is apolymerization reaction product of: a polydimethylsiloxane (PDMS) havinga pendant or terminal functional group selected from a group offunctional groups consisting of epoxy functional groups, vinylfunctional groups, and acrylate functional groups; and an initiator. 11.The flexible-to-rigid tube as recited in claim 10, wherein the PDMS hasa pendant or terminal epoxy functional group, wherein the initiator isan onium photoinitiator, and wherein the polymerization reaction occursupon exposure of the flexible-to-rigid tube to actinic radiation. 12.The flexible-to-rigid tube as recited in claim 9, wherein thecross-linked network is a polymerization reaction product of: triallylisocyanurate (TAIC); and an initiator selected from a group ofinitiators consisting of free radical photoinitiators and thermalinitiators.
 13. The flexible-to-rigid tube as recited in claim 12,wherein the initiator comprises a free radical photoinitiator includingbenzoin, and wherein the polymerization reaction occurs upon exposure ofthe flexible-to-rigid tube to actinic radiation.
 14. Theflexible-to-rigid tube as recited in claim 12, wherein the initiatorcomprises a thermal initiator including a benzoyl peroxide orazobisisobutyronitrile, and wherein the polymerization reaction occursupon exposure of the flexible-to-rigid tube to heat.
 15. Theflexible-to-rigid tube as recited in claim 12, wherein the TAIC and theinitiator are incorporated into a PVC-based tubing material.
 16. Amethod of fabricating a cooling plate assembly for transferring heatfrom a plurality of electronic components mounted on a circuit board,comprising the steps of: providing a circuit board having a top surfaceand a bottom surface; positioning a first cooling plate over and inthermal contact with at least one electronic component mounted on thetop surface of the circuit board and having a thermal dissipationchannel extending through a portion thereof; positioning a secondcooling plate positioned and in thermal contact with at least oneelectronic component mounted on the top surface of the circuit board andhaving a thermal dissipation channel extending through a portionthereof; interconnecting the thermal dissipation channel of the firstcooling plate and the thermal dissipation channel of the second coolingplate using a flexible-to-rigid tube, wherein the interconnecting stepincludes the step of routing the flexible-to-rigid tube in a flexiblestate between the thermal dissipation channel of the first cooling plateand the thermal dissipation channel of the second cooling plate;rigidizing the flexible-to-rigid tube after the interconnecting step,wherein the rigidizing step includes the step of forming a cross-linkednetwork to change the flexible-to-rigid tube from the flexible state toa rigid state.
 17. The method as recited in claim 16, wherein thecross-linked network is a polymerization reaction product of: apolydimethylsiloxane (PDMS) having a pendant or terminal functionalgroup selected from a group of functional groups consisting of epoxyfunctional groups, vinyl functional groups, and acrylate functionalgroups; and an initiator.
 18. The method as recited in claim 17, whereinthe PDMS has a pendant or terminal epoxy functional group, wherein theinitiator is an onium photoinitiator, and wherein the step of forming across-linked network includes the step of exposing the flexible-to-rigidtube to actinic radiation.
 19. The method as recited in claim 16,wherein the cross-linked network is a polymerization reaction productof: triallyl isocyanurate (TAIC); and an initiator selected from a groupof initiators consisting of free radical photoinitiators and thermalinitiators.
 20. The method as recited in claim 19, wherein the initiatorcomprises a free radical photoinitiator including benzoin, and whereinthe step of forming a cross-linked network includes the step of exposingthe flexible-to-rigid tube to actinic radiation.
 21. The method asrecited in claim 19, wherein the initiator comprises a thermal initiatorincluding a benzoyl peroxide or azobisisobutyronitrile, and wherein thestep of forming a cross-linked network includes the step of exposing theflexible-to-rigid tube to heat.
 22. A method of utilizing aflexible-to-rigid tube, comprising the steps of: routing theflexible-to-rigid tube in a flexible state; rigidizing theflexible-to-rigid tube after the routing step, wherein the rigidizingstep includes the step of exposing the flexible-to-rigid tube to actinicradiation or heat to change the flexible-to-rigid tube from the flexiblestate to a rigid state via formation of a cross-linked network, andwherein the cross-linked network includes at least one of a silicone ortriallyl isocyanurate (TAIC).